A voltage-controlled attenuator with continuously adjustable attenuation

Abstract

The present invention belongs to the field of microwave technology, and particularly relates to a voltage-controlled attenuator with continuously adjustable attenuation amount, which includes a printed circuit board (PCB), a transition structure, and a direct current pin. On the printed circuit board (PCB), there are a transmission line, two grounding structures, PIN diodes, chip capacitors, gold wires, and tapered inductors; among them, the PIN diodes, chip capacitors, and gold wires form an integral body, which is called the first component; by controlling the voltage of the PIN diodes in the first component to continuously change, the equivalent resistance of the PIN diodes is continuously changed, so as to realize the continuous adjustment of the attenuation amount of the voltage-controlled attenuator. In cooperation with the introduction of gold wires in the first component and the use of the inductance performance presented by the gold wires, the parasitic capacitance of the PTN diodes is compensated, enabling it to have better return loss and a wider operating frequency band.

Description

Technical Field

[0001] The present invention belongs to the field of microwave technology, and particularly relates to a voltage-controlled attenuator with continuously adjustable attenuation amount. Background Art

[0002] The function of an attenuator in a circuit system is to attenuate electromagnetic signals, control the signal magnitude to make it reach the required level in the circuit, and can also be used to improve the characteristics of the matching network port to ensure the matching performance between different circuit modules.

[0003] Attenuators can be classified into: passive attenuators and active attenuators according to their working characteristics. Passive attenuators usually do not introduce additional power supply noise or harmonics; active attenuators can achieve the function of actively adjusting the signal amplitude and have a wider adaptability.

[0004] Attenuators can be classified into: fixed attenuators and adjustable attenuators according to the attenuation form. Fixed attenuators usually construct a specific type of resistor network with resistors of different resistance values. The π-type structure or T-type structure is a common structure type, and it has stable attenuation performance in a very wide working frequency band. Adjustable attenuators can be further divided into: mechanical adjustment attenuators, programmed attenuators, voltage-controlled attenuators, etc. Mechanical adjustment attenuators achieve different attenuation values by mechanically adjusting the circuit structure or resistor resistance; programmed attenuators usually consist of multiple fixed attenuation networks in series and single-pole double-throw switches, and complete logical control through an additional circuit to achieve the circuit function of the attenuator, but additional power supply and control ports are required; voltage-controlled attenuators can usually continuously adjust the attenuation amount, and compared with mechanical adjustment attenuators and programmed attenuators, the number of control ports can be reduced.

[0005] The existing research on voltage-controlled attenuators with continuously adjustable attenuation amount is as follows:

[0006] Ruofeng Xu et al. conducted an approximate analysis of a slotted substrate integrated waveguide with periodically loaded elements in R.F.Xu, A.J.Farrall, P.R Young.Analysis of loaded substrate integrated waveguides and attenuators[J].IEEE microwave and wireless components letters, 2013, 24(1):62 - 64. The transverse resonance technique was used for the design of the attenuator. PIN diodes were coupled to the waveguide slots, and the resistance was changed by changing the bias, generating a constant variable attenuation within the frequency band. This attenuator can provide variable attenuation from 2 to 25 dB in the range of 3 - 5 GHz, and the return loss is better than 15 dB.

[0007] Gabriela Luciani et al. in G. Luciani, J Bornemann. Half-Mode SIW Variable PIN Diode Attenuator [C] / / 2019 13th European Conference on Antennas and Propagation (EuCAP). IEEE, 2019: 1 - 5. presented a half-mode substrate integrated waveguide (HMSIW) variable attenuator operating in the frequency range of 6 GHz to 10 GHz. By adjusting the DC bias levels applied to four surface-mounted PIN diodes, different levels of attenuation were achieved, with a maximum attenuation of 6 dB.

[0008] Saavedra et al. in C. E. Saavedra, Y. Zheng Ring-hybrid microwave voltage-variable attenuator using HFET transistors [J]. IEEE transactions on microwave theory and techniques, 2005, 53(7): 2430 - 2434. introduced a voltage-controlled attenuator circuit based on field-effect transistors (FETs). The input signal first enters a power divider where signals of 0 and 180 degrees are generated. The 0-degree signal is transmitted through a fully open common-gate FET with its gate voltage set to 0 V. The 180-degree signal enters another common-gate transistor biased in the triode region. By changing the gate voltage of the second FET, the amplitude of the 180-degree signal can be changed. The in-phase and out-of-phase signals are added at the output to achieve variable attenuation. The attenuator achieved variable attenuation of 6 to 30 dB in the frequency range of 3.0 to 3.4 GHz.

[0009] C. Shireesha et al. introduced a medium-power voltage variable attenuator based on PIN diodes implemented on a microstrip line, with a topology based on a 90-degree hybrid coupler. A single hybrid coupler attenuator can be used for broadband operation, and the design of the dual hybrid coupler eliminates the ripple response in the high attenuation state, thereby increasing the dynamic range. The paper proposed two medium-power PIN diode voltage variable attenuators with a working frequency range of 9.1 - 9.6 GHz, and their attenuation ranges are approximately 15 dB and 28 dB respectively. The return loss is 10 dB across the entire frequency range.

[0010] In the practical application of microwave circuits, compared with fixed attenuators, due to factors such as the parasitic effects of active components, there are certain gaps in performance indicators such as the operating frequency and attenuation of voltage-controlled attenuators with adjustable attenuation. The main problems existing in current voltage-controlled attenuators are as follows:

[0011] 1. The operating frequency is relatively low and the range is narrow, and the operating frequency does not exceed 10 GHz.

[0012] 2. Some attenuators are large in volume and limited in attenuation. For example, the maximum attenuation of the voltage-controlled attenuator disclosed by Gabriela Luciani et al. is only 6 dB.

[0013] 3. The return loss of some needs to be optimized, such as the voltage-controlled attenuator disclosed by C. Shireesha et al.

[0014] Therefore, designing a miniaturized voltage-controlled attenuator with a higher operating frequency band and a larger attenuation is of positive significance for the development of attenuators. Summary of the Invention

[0015] The purpose of the present invention is to provide a voltage-controlled attenuator with continuously adjustable attenuation, having low return loss, small volume, higher operating frequency and wider frequency range.

[0016] To achieve the above purpose, the present invention adopts the following technical solutions:

[0017] A voltage-controlled attenuator with continuously adjustable attenuation includes a printed circuit board (PCB), a transition structure, and a direct current pin.

[0018] On the printed circuit board (PCB), there are a transmission line, two grounding structures, PIN diodes, chip capacitors, gold wires for compensating the parasitic capacitance of the PIN diodes, and tapered inductors. The two grounding structures are the first grounding structure and the second grounding structure respectively. The first grounding structure is symmetric with the second grounding structure with respect to the transmission line and is arranged at a distance from the transmission line; the PIN diodes, chip capacitors, and gold wires for compensating the parasitic capacitance of the PIN diodes form an integral body, which is called the first component; the first component is arranged at intervals along the length direction of the transmission line from one end to the other end and does not cover the entire transmission line; in the first component: one end of the PIN diode is connected to the transmission line, and the other end is connected to the first grounding structure; the chip capacitor is arranged in parallel with the PIN diode and is bonded to the transmission line through conductive adhesive; the gold wire is led out from the chip capacitor and connected to the first grounding structure; the tapered inductor is arranged on the second grounding structure, behind the last first component, with one end connected to the transmission line and the other end connected to the DC power pin;

[0019] The transition structure is behind the last first component, with one side extending to the edge of the second grounding structure and the other end away from the printed circuit board (PCB). There are two transition structures;

[0020] The DC power pin is arranged between the two transition structures and is spaced from the transition structures. The DC power pin and the two transition structures are connected by decoupling capacitors.

[0021] Further, the first components are arranged at equal intervals along the length direction of the transmission line from one end to the other end.

[0022] Further, the decoupling capacitors include 1uF decoupling capacitors and 100pF decoupling capacitors.

[0023] Further, the first grounding structure adopts the structure of Conductor-Backed Coplanar Waveguide (CBCPW), on which there are three rows of vias penetrating the printed circuit board (PCB); to ensure better realization of the AC grounding effect and to confine the range of the electric field, the via arrangement is convenient for the soldering of the PIN diodes and gold wires; the second grounding structure is exactly the same as the first grounding structure.

[0024] Even further, the vias are rounded rectangular vias.

[0025] Further, the transmission line is a 50Ω microstrip line.

[0026] Further, the line width of the transmission line is W, and the distance between it and the grounding structure is W gap ; in the grounding structure, the radius of the rounded rectangular via is R via and the via length is L via and the distance between adjacent rounded rectangular vias is Lgap ; The distance between PIN diodes in two adjacent first components is L λg / 4 , where λg is the transmission line wavelength and the length of the gold wire is L.

[0027] The working principle of the voltage-controlled attenuator of the present invention is as follows: In the prior art, the Chinese patent with the publication number CN115714249A discloses an invention named "A Step-Type Passive Attenuator Realized on a Ceramic Substrate", and in this patent, it is disclosed that resistors are placed at intervals of a quarter wavelength of the transmission line and connected to the transmission line and the grounding structure, so that attenuation can be achieved in the resistor when a microwave signal passes through the transmission line. Specifically:

[0028] In a radio frequency circuit system, to meet its impedance matching, the characteristic impedance of the transmission line is selected to be 50Ω. Normalize the attenuation matrix A:

[0029]

[0030] Convert the normalized A matrix into a scattering parameter matrix:

[0031]

[0032]

[0033]

[0034]

[0035] a 11 、a 12 、a 21 、a 22 represent the elements in the matrix;

[0036] According to the above calculation formula, the port standing wave of the attenuator is inversely proportional to the resistance value of the access resistor, that is, a smaller access resistor will increase the port standing wave. While increasing the loss of the transmission line, the resistance path also increases the degree of mismatch of the transmission structure. It can be seen that this type of attenuator improves the attenuation amount of the attenuator at the cost of increasing the mismatch degree, and at the same time as the insertion loss increases, the return loss also increases. That is to say, this type of attenuator cannot theoretically achieve perfect port matching.

[0037] Based on the above design principle of the step-type adjustable attenuator, the present invention utilizes the characteristic that the microwave resistance of the PIN diode changes with the bias voltage, replaces the original fixed resistor with a PIN diode, and by controlling the continuous change of the voltage of the PIN diode, the equivalent resistance of the PIN diode also changes continuously, so as to realize a voltage-controlled attenuator with continuously adjustable attenuation amount.

[0038] However, due to the parasitic capacitance of the PIN diode, the impact on the circuit cannot be ignored. To overcome this problem, the present invention uses a gold wire to bridge both sides of the PIN diode to simulate the inductance function and compensate for the parasitic capacitance. The length of the gold wire is calculated according to the following formula:

[0039]

[0040]

[0041] where d is the diameter of the gold wire, f is the operating frequency, and ρ is the conductivity of the gold wire.

[0042] The compensated PIN diode can be approximated as a voltage-controlled resistor. When the bias voltage is large, the matching degree decreases and the attenuation increases; relatively, when the bias voltage is small, the matching degree increases and the attenuation decreases. It should be noted at this time that since both the AC signal on the transmission line and the DC bias voltage of the given PIN diode are loaded through the microstrip line, it is necessary to adopt a CBCPW grounding structure to achieve simultaneous grounding of DC and AC and "isolate" the given DC bias voltage and AC signal in the circuit.

[0043] In summary, after adopting the above technical solutions, the present invention has the following advantages:

[0044] (1) The present invention uses a PIN diode for attenuation. The resistance of the PIN diode is controlled by its bias voltage, and the attenuation value of the attenuator can be continuously adjusted by voltage, and the adjustable range of the attenuation value is wide.

[0045] (2) The present invention uses a gold wire to compensate for the parasitic capacitance of the PIN diode, making the return loss performance of the attenuator better than that of the stepped passive attenuator and having a wide operating frequency band.

[0046] (3) The present invention uses a printed circuit board, and the components constituting the attenuator are easy to obtain, with a simple structure and low cost. Description of the Drawings

[0047] Figure 1 is the front view of the attenuator structure in Embodiment 1;

[0048] Figure 2 is a partially enlarged schematic diagram of the gold wire compensation circuit;

[0049] Figure 3 is the physical diagram of the attenuator in Embodiment 1, where (a) is a partially enlarged view of devices such as the PIN diode and the gold wire, and (b) is a partially enlarged view of devices such as the tapered inductor and the DC power pin;

[0050] Figure 4 is the S of the attenuator when the PIN diode is simplified to a pure resistor and different resistance values (100 - 400 Ω) are taken21 With S 22 Simulation result diagram;

[0051] Figure 5 When the PIN diode is simplified to a parallel combination of a capacitor and a resistor, the S of attenuators with different resistance values (100 - 400 Ω) 21 With S 22 Simulation result diagram;

[0052] Figure 6 When the PIN diode is simplified to a parallel combination of a capacitor and a resistor and a compensation inductor is introduced, the S of attenuators with different resistance values (100 - 400 Ω) 21 With S 22 Simulation result diagram;

[0053] Figure 7 The S of attenuators under different bias voltages (0.7 - 1.05 V) 21 With S 22 Measured result diagram;

[0054] Reference numerals: 1 is a printed circuit board PCB, 2 is a transmission line, 3 is a grounding structure, 4 is a PIN diode, 5 is a chip capacitor, 6 is a gold wire, 7 is a conical inductor, 8 is a DC power pin, 9 is a 1 uF decoupling capacitor, 10 is a 100 pF decoupling capacitor. Detailed implementation manners

[0055] The following uses specific specific examples to illustrate the implementation manners of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content mentioned in this specification. The present invention can also be implemented or applied through other different specific implementation manners, and various details in this specification can also be evolved based on different viewpoints and applications without departing from the spirit of the present invention.

[0056] Example 1

[0057] As Figure 1 shown, a voltage-controlled attenuator with continuously adjustable attenuation provided in this embodiment includes

[0058] Printed Circuit Board (PCB) 1, transmission line 2, AC grounding structures 3 on both sides of the transmission line, PIN diode 4, chip capacitor 5, conical inductor 7 for supplying DC operating voltage to the given PIN diode 4, DC power pin 8, 1uF decoupling capacitor 9, 100pF decoupling capacitor 10. Among them, the transmission line 2 is used to transmit signals; the PIN diode 4 is used to attenuate the transmission line signals; the chip capacitor 5 is used for isolating DC control signals and passing AC signals at the same time; it is used to separate the DC control signal from; the grounding structure 3 realizes the grounding of DC and AC signals; the DC power pin 8 is used to supply DC operating voltage to the PIN diode 4; the conical inductor 7 is used to pass DC signals and block AC signals. The 1uF decoupling capacitor 9 and the 100pF decoupling capacitor 10 are used to filter the DC control signals.

[0059] After simplifying the PIN diode in the above structure into a single resistor, the circuit is modeled and simulated, and an attenuator with excellent performance can be designed. The S of this attenuator 21 and S 22 The simulation results are as Figure 4 shown. Since the PIN diode has parasitic capacitance and the capacitance value of the parasitic capacitance will change with the bias voltage, although the capacitance value of the parasitic capacitance is in the fF order, from Figure 4 the shown simulation results, it can be seen that such simplification ignores the influence of the parasitic capacitance on the circuit, thus affecting the high-frequency response characteristics of the attenuator.

[0060] After simplifying the PIN diode in the model into a parallel combination of a resistor and a small capacitor, the circuit is modeled and simulated again. The simulation results of the designed attenuator are as Figure 5 shown, indicating that due to the existence of the parasitic capacitance, the circuit structure deviates from the original design, and the original theoretical analysis has limitations. Therefore, additional inductive circuits are needed to compensate for the influence of the parasitic capacitance on the circuit.

[0061] Since the operating frequency of common inductor components is limited, and in addition, according to theoretical knowledge and engineering experience, gold wires will exhibit inductive characteristics. Based on this characteristic, in this embodiment, gold wires are used to bridge both sides of the diode to simulate the inductance performance to compensate for the parasitic capacitance of the PIN diode. After simplifying the compensated PIN diode into a parallel combination of a capacitor, an inductor, and a resistor, the circuit is modeled and simulated again, and the optimization process is completed. The simulation results are as Figure 6 shown. It shows that the PIN diode compensated by introducing the gold wire 6 can be approximated as a voltage-controlled resistor.

[0062] According to the operating frequency range of the attenuator in this embodiment, the printed circuit board PCB1 uses the substrate Rogers4350, the thickness of the dielectric layer is 0.168 mm, and the thickness of the metal layer is 40 μm. The transmission line 2, the grounding structure 3, and the DC pin 8 are copper-gold-plated metal layers formed by PCB etching. The line width of the transmission line 2 is determined according to the 50Ω impedance on the PCB substrate. There are two grounding structures 3, namely the first grounding structure and the second grounding structure, and the first grounding structure and the second grounding structure are symmetric about the transmission line 2. The first grounding structure adopts a structure similar to Conductor-Backed Coplanar Waveguide (CBCPW), and is provided with three rows of rounded rectangular vias penetrating the printed circuit board PCB1; to ensure a better AC grounding effect and confine the range of the electric field; for the convenience of the assembly of the PIN diode 4 and the gold wire 6, the rounded rectangular vias near the transmission line 2 are arranged in a staggered manner with the middle row of rounded rectangular holes, and the row of rounded rectangular vias far from the transmission line 2 is arranged in the same way as the middle row of rounded vias. The second grounding structure is exactly the same as the first grounding structure.

[0063] The DC pin is located outside the transmission line and the grounding structure and on one side edge of the printed circuit board PCB1. The DC pin 8 includes a rectangular sheet located between two transition structures and having a gap with the transition structures and the printed circuit board PCB1. The printed circuit board PCB1 and the two transition structures form a three-sided surrounding structure for the rectangular metal sheet. The PIN diode 4, the chip capacitor 5, and the gold wire 6 for compensating the parasitic capacitance of the PIN diode form a whole, which is called the first component. The direction along the long side of the transmission line 2 on the printed circuit board PCB1 is defined as the x direction, and the direction along the wide side of the transmission line 2 is defined as the y direction. The first components are arranged at equal intervals along the length direction of the transmission line 2 from one end to the other end and do not cover the long side of the transmission line 2. In the first component: one end of the PIN diode 4 is connected to the transmission line 2, and the other end is connected to the first grounding structure. To achieve a better grounding effect, its negative electrode is closely attached to the edge of the rounded rectangular via of the first grounding structure; the chip capacitor 5 is arranged in parallel with the PIN diode 4 and is bonded to the transmission line 2 through a conductive adhesive.

[0064] As Figure 2 shown, the PIN diode is bonded between the transmission line and the grounding structure with a conductive adhesive; the chip capacitor is closely assembled on the transmission line with the diode; one end of the gold wire 6 needs to be connected to the chip capacitor, and the other end is connected to the first grounding structure. If the inductance is large, it can be connected to the metal layer between the rounded rectangular vias near the transmission line. If the inductance is small, it can be welded to the metal layer between the middle and the rounded rectangular vias far from the transmission line. Except for the row of rounded rectangular vias near the transmission line, the other two rows of rounded rectangular vias are arranged in the same way so that the middle metal layer forms a whole, which is more convenient for the assembly of the gold wire.

[0065] In this embodiment, the length L of the gold wire 6 is calculated using the following formula:

[0066]

[0067]

[0068] Where d is the diameter of the gold wire, f is the operating frequency, and ρ is the conductivity of the gold wire.

[0069] In Embodiment 1, there are 11 groups of the first components, and the adjacent PIN diodes are spaced by L λg / 4 laid. The gold wire is connected to the metal layer between the via of the transmission line and the via of the middle row, as Figure 3 (a) shows.

[0070] To ensure the feeding of the bias voltage of the PIN diode, a tapered inductor is connected between the DC power pin and the transmission line, and a decoupling capacitor is also introduced at the tapered inductor to further filter out clutter and interference. In the embodiment, two groups of 1uF capacitors and 100pF capacitors are selected.

[0071] The tapered inductor 7 is arranged on the second grounding structure, behind the last first component. One end of it is connected to the transmission line 2, and the other end is connected to the DC power pin 8. Such an arrangement can effectively suppress the noise of the power supply and prevent the useful signal from being fed into the power supply, etc. To better filter out clutter and interference, a decoupling capacitor is also introduced at the tapered inductor 7 in this embodiment. Specifically: between the same side of the rectangular sheet and its adjacent transition structure, it is connected by a 1uF decoupling capacitor 9 and a 100pF decoupling capacitor, and the non-surrounded surface of the rectangular sheet is connected to the outside through a metal strip.

[0072] After simulation and optimization with the electromagnetic simulation software Ansoft HFSS, the optimal parameter dimensions are obtained as shown in the following table:

[0073] Table 1 Attenuator Parameter Table

[0074] Width W of the transmission line 0.31 mm <![CDATA[The distance W between the transmission line and the grounding structure gap > 0.35 mm <![CDATA[Adjacent PIN diode spacing L λg / 4 > 2.00 mm <![CDATA[Length L of the runway-shaped via hole via > 1.70 mm <![CDATA[Adjacent track-shaped via hole pitch L gap > 0.30 mm Length L of the gold wire 1.64 mm Diameter Φ of the gold wire 25.0 μm <![CDATA[Radius R of the runway-shaped via hole via > 0.25 mm

[0075] In the measured results, the attenuation value can be adjusted by voltage. As Figure 7 shown, when the bias voltage range is from 0.7 to 1.05V, the attenuator has good performance. The return loss of the attenuator is better than -15dB in all frequency bands within the operating frequency band from 10.5GHz to 19GHz. The insertion loss can achieve continuous change from -2dB to -20dB. It can be seen that in the voltage-controlled attenuator with continuously adjustable attenuation amount provided in this embodiment, by introducing the gold wire 6 to compensate for the parasitic capacitance of the PIN diode 4

[0076] The above embodiments are only illustrative of the principles and effects of the present invention and are not intended to limit the present invention. Any person familiar with this technology can modify or change the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or changes made by those with ordinary knowledge in the technical field without departing from the spirit and technical idea disclosed by the present invention should still be covered by the claims of the present invention.

Claims

1. A voltage-controlled attenuator with continuously adjustable attenuation amount, comprising a printed circuit board (PCB), a transition structure, and a direct current pin, characterized in that: On the printed circuit board (PCB), there are a transmission line, two grounding structures, PIN diodes, chip capacitors, gold wires for compensating the parasitic capacitance of the PIN diodes, and tapered inductors; the two grounding structures are respectively a first grounding structure and a second grounding structure, the first grounding structure and the second grounding structure are symmetric about the transmission line and are arranged at a distance from the transmission line; the PIN diodes, chip capacitors, and gold wires for compensating the parasitic capacitance of the PIN diodes form an integral body, called the first component; the first component is arranged at intervals along the length direction of the transmission line from one end to the other end and does not cover the entire transmission line; in the first component: one end of the PIN diode is connected to the transmission line, and the other end is connected to the first grounding structure; the chip capacitor is arranged in parallel with the PIN diode and is bonded to the transmission line through conductive glue; the gold wire is led out from the chip capacitor and is connected to the first grounding structure; the tapered inductor is arranged on the second grounding structure, behind the last first component, one end of which is connected to the transmission line and the other end is connected to the direct current pin; The transition structure is behind the last first component, one side of which extends to the edge of the second grounding structure and the other end is away from the printed circuit board (PCB), and there are two transition structures; The direct current pin is arranged between the two transition structures and is spaced from the transition structures, and the direct current pin and the two transition structures are connected by decoupling capacitors.

2. The voltage-controlled attenuator with continuously adjustable attenuation according to claim 1, wherein: The first component is arranged at equal intervals along the length direction of the transmission line from one end to the other end.

3. The voltage-controlled attenuator with continuously adjustable attenuation amount according to claim 1, characterized in that: The decoupling capacitors include 1uF decoupling capacitors and 100pF decoupling capacitors.

4. The voltage-controlled attenuator with continuously adjustable attenuation amount according to claim 1, characterized in that: The first grounding structure adopts a CBCPW structure, on which there are three rows of vias penetrating the printed circuit board (PCB); to ensure a better AC grounding effect and restrict the range of the electric field, the via arrangement is convenient for the soldering of the PIN diodes and gold wires; the second grounding structure is exactly the same as the first grounding structure.

5. A voltage-controlled attenuator with continuously adjustable attenuation amount according to claim 4, characterized in that: The via is a rounded rectangular via.

6. The voltage-controlled attenuator with continuously adjustable attenuation amount according to claim 1, wherein: The transmission line is a 50Ω microstrip line.

7. A voltage-controlled attenuator with continuously adjustable attenuation amount according to any one of claims 1 to 6, characterized in that: The line width of the transmission line is W, and its distance from the grounding structure is W gap ; In the grounding structure, the radius of the rounded rectangular via is R via , and the via length is L via , and the distance between adjacent rounded rectangular vias is L gap ; The distance between PIN diodes in two adjacent first components is L λg / 4， where λg is the transmission line wavelength, and the length of the gold wire is L.

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